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This report concerns the extension period for data down-load of the RA4 project with the same title, which was granted on 1/4/2016. This activity thus follows the final re-port for the proposal [1], which was submitted in 2017. During the report period, processing of the data already downloaded was finalized, and data on other test sites were downloaded, thanks to the extension of the image quota as-signed to the project. This report is therefore divided into two parts. We first summarize the results obtained by processing ALOS data over the Tavoliere plain in the Apulia Region, Southern It-aly. Then, we describe the data and the first, preliminary processing steps performed over the remaining test sites (the Zambesi river in Southern-East Africa, and the Hy-malayan glacier in the Gangdise Mountains, China).

The shorter repeat cycle (6 days since October 2016) and regularity of acquisitions of Sentinel-1A/B with respect to earlier European Space Agency (ESA) satellites with C-band sensors (ERS1/2, ENVISAT) represent the key advantages for the research-oriented and practical applications of multi-temporal interferometry (MTI). The applicability of the Interferometric Wide Swath acquisition mode of Sentinel-1 (images covering a 250 km swath on the ground) to regional scale slope instability detection through MTI has already been demonstrated, e.g., via studies of landslide-prone areas in Italy. Here we focus on the potential of Sentinel-1 data for local (site-specific), MTI-based monitoring and capturing pre-failure signs of slope instability, by exploiting the Persistent and Distributed Scatterers processing capability of the SPINUA algorithm. In particular, we present an example of a retrospective study of a large (over 2 km long) landslide, which took place in 2016 in an active open-cast coal mine in central Europe. This seemingly sudden failure caused destruction of the mining equipment, blocked the mining operations thereby resulting in significant economic losses. For the study, we exploited over 60 Sentinel-1A/B images acquired since November 2014. The MTI results furnished a valuable overview of the ground instability/stability conditions within and around the active mine, even though considerable spatial gaps in information were encountered due to surface disturbance by mining operations. Significantly, the ground surface displacement time series revealed that the 2016 slope failure was preceded by very slow (generally 1-3 cm/yr) creep-like deformations, already present in 2014. The MTI results also indicated that the slope experienced a phase of accelerated movement several weeks prior to the landslide event. Furthermore, the spatio-temporal analysis of interferometric coherence changes in the unstable area (mapped on Sentinel-2 Bottom Of Atmosphere reflectance images processed by using the ESA Sen2Cor processor), indicated a sharp coherence loss in the last few weeks before the slope collapse. The availability of more frequent measurements represents a key improvement for MTI-based ground surface displacement monitoring and this will better support research on slope destabilization processes over time and, ultimately, on slope failure forecasting.

On March 11th, 2011, 05:46 UTC, a giant earthquake of magnitude Mw=9.0 occurred off the Pacific coast of Tohoku, Honshu Island, Japan. Massive damage has been reported, mainly related to the subsequent tsunami. In this work we present first results concerning the displacement induced by the Tohoku-oki earthquake by using ASAR ENVISAT data acquired few days before and after the event. The work points out the reliability of ASAR ENVISAT data to provide interferometric-based displacement field even though the satellite is recently came into a new operative phase with degraded orbital control and SAR data were processed in an emergency framework soon after the acquisition without precise orbital records. After removing artefacts due to strong orbital errors, the interferometric deformation pattern is mainly related to the coseismic displacement and it results comparable to that provided by the GEONET GPS network which has an unique density of in situ measurements found elsewhere in the world.

The Multi-Chromatic Analysis, as introduced in [1], uses interferometric pairs of SAR images processed at range sub-bands and explores the phase trend of each pixel as a function of the different central carrier frequencies. The phase of stable scatterers evolves linearly with the sub-band central wavelength, the slope being proportional to the absolute optical path difference. Unlike the standard "monochromatic" InSAR approach, this technique allows performing spatially independent and absolute topographic measurements, if the attention is focused on single targets exhibiting stable phase behaviour across the frequency domain. Potential applications for the study of frequency-stable targets include topographic measurement, atmospheric research, and urban monitoring. Through a simplified model [2], we obtained a first evaluation of the impact of the MCA processing parameters on the height estimation performances. A total bandwidth of at least 300 MHz seems to be required to provide reliable results. Thus, the technique appears optimally suited for the new generation of satellite sensors, which operate with larger bandwidths than previously available instruments, generally limited to few tens of MHz. SAR sensors such as those mounted on TerraSAR-X (TSX) or COSMO-SkyMed (CSK) spacecraft, all pose great expectations on the potential use of multi-chromatic methods. The practical feasibility of the technique was demonstrated in [2] by using a set of SAR data collected by the airborne AES-1 radar interferometer, operating at X-band by multi-channel electronics, which provides a total radar bandwidth of 400 MHz. A first successful application of the technique to satellite data was also shown in [3] by using a spotlight interferometric pair of images acquired by TSX on the well-known Uluru monolith in Australia. In the present work, we illustrate results obtained through MCA processing on spaceborne SAR data acquired by the CSK constellation both on Parkfield in California (USA), and on the Uuluru monolith. A CSK tandem pair acquired on the Uluru test site was used to validate the MCA-based height measurements by using a digital surface model (DSM) derived from optical stereo imagery captured at 15 cm resolution. The same dataset was also processed to validate the theoretical analysis [2] developed to assess the performance of the MCA with respect to the radiometric parameters involved in the processing (total bandwidth, sub-bandwidth, number of sub bands). The MCA technique introduces the concept of frequency-stable targets (PSfd), i.e. objects exhibiting stable radar returns across the frequency domain. This concept is complementary to that of temporal stability, which is at the base of persistent scatterers interferometry (PSI) techniques [4]. In PSI applications, stable targets (PS) are recognized as those exhibiting temporal stability through a stack of tens of SAR images. It is then natural to try to compare the two concepts, examining the assumptions which form the basis of the two definitions, and evaluating the respective characteristics of the two populations, with the final goal of ascertaining if any synergy can be identified between the two types of object. The Parkfield test site was used to attempt this comparison. A stack of 33 spotlight CSK acquisition was used to perform PSI through the SPINUA PSI algorithm [5]. Four tandem pairs selected within the multitemporal dataset were processed through MCA in order to derive four sets of PSfd to compare to the PS targets. An ad hoc processing scheme was developed to derive PSI products by processing the same range sub-bandwidth used by the MCA in order to guarantee the same scattering conditions. The populations of PSfd and "temporal" PS were compared and preliminary considerations provided concerning the scattering properties of the targets selected by the two criteria. Finally, we present potentials of MCA to measure absolute ranging by using a single SAR image. References [1]N. Veneziani, F. Bovenga, A. Refice, "A wide-band approach to absolute phase retrieval in SAR interferometry", Multidimensional Systems and Signal Processing, Vol. 14(1-2), pp. 183-205, 2003. [2]F. Bovenga, V. M. Giacovazzo, A. Refice, N. Veneziani, R. Vitulli, "Multi-Chromatic Analysis of InSAR data: validation and potential", Proceedings of FRINGE 2009, ESA-ESRIN, Frascati, Italy, Nov.30 - Dec. 4, 2009. [3]F. Bovenga, V. M. Giacovazzo, A. Refice, D. O. Nitti, N. Veneziani, "Interferometric multi-chromatic analysis of high resolution X-band data". Proceedings of FRINGE 2011, ESA-ESRIN, Frascati, Italy, Sept. 19-23, 2011. [4]A. Ferretti, C. Prati, and F. Rocca, "Permanent Scatterers in SAR Interferometry", IEEE Trans. Geosc. Remote Sens., vol. 39(1), pp. 8-20, 2001. [5]F. Bovenga, A. Refice, R. Nutricato, L. Guerriero, and M. T. Chiaradia, "SPINUA: a flexible processing chain for ERS/ENVISAT long term interferometry," in Proc. 2004 Envisat & ERS Symposium, Salzburg, Austria, 6-10 September, 2004.

The PSI (Persistent Scatterer Interferometry) processing of ENVISAT ASAR data (period 2003-2010) provided spatially dense information (more than 400 PS/km2) on ground surface displacements in Lanzhou, capital of Gansu Province, NW China. The geomorphological and geological context of the local Yellow River valley indicate that the lower, flat areas with floodplain and valley-fill deposits (Holocene terraces with mainly reworked loess at the surface) are stable, whereas some higher, gently sloping valley sides appear locally unstable, particularly where the Late Pleistocene terraces are covered by young aeolian (Malan) loess. The PS velocity data suggest that the relative susceptibility to ground and slope instabilities is the highest on the 4th and 5th order river terraces. This is consistent with the presence of collapsible Malan loess and recent land use of these terraces involving irrigation and construction.

The present study is aimed at investigating the potentialities of the COSMO/SkyMed (CSK) constellation for ground elevation measurement with particular attention devoted to the impact of the improved spatial resolution wrt the previous SAR sensors. Assuming no movement and successful orbital error removal, the main problem in height computation derives from the atmospheric artifacts (APS). Different strategies can be adopted to filter out this signal: 1.By processing stack of images and through advanced multi-temporal interferometric analysis, it is possible to infer with sub-metric precision the height of targets which behave coherently in time (persistent scatterers). These techniques allow to filter out the atmospheric signal thanks to its decorrelation in time and correlation in space. The main drawback is related to the availability of coherent scatterers on the scene. High resolution sensors (as CSK) allow to increase the density of the measurable targets. 2.By using tandem-like high resolution interferometric pairs and a reference low resolution DEM, it is possible to filter the differential phase field in order to remove the atmospheric artifacts. The filtered InSAR phase may hence improve the accuracy of the original DEM. 3.Through Numerical Weather Models (NWM), it is possible to estimate the InSAR phase related to the interaction between microwave and atmosphere. In the present work we explored all the mentioned strategies for APS mitigation. The selected test site was Parkfield (California, USA), where a consistent number of both Stripmap HIMAGE and Enhanced Spotlight right-descending HH acquisitions are available with very close incidence angles. Both dataset were hence used to experiment the reliability of multi temporal analysis for height computation (strategy #1). Our results are in line with indications found in recent literature, proving the potential of PSI to provide sub-metric precision of height measurements. Satisfactory performances may be achieved also by properly filtering the differential interferometric phase derived by using CSK tandem-like pairs (strategy #2). In particular, when normal the baselines exceed 300 m, it is possible to derive DEMs fulfilling the HRTI Level 3 specifications on the relative vertical accuracy. On the contrary, the mitigation of atmospheric artifacts through NWM (strategy #3) is still uncertain especially for X-band InSAR. Our preliminary results confirm the indications coming from other similar studies: NWM are effective for the long wavelengths (>20 km) and for vertical stratification which depends on the hydrostatic component of the troposphere, while, when dealing with the turbulent component of the low troposphere, this approach is unfeasible. SAR processing indeed requires millimetric accuracy in the zenith atmospheric delay while the outcomes of the NWM are in the order of centimeters, as confirmed by the validation performed through independent RAOBS and GPS ZTD data. Possible improvements can derive by the assimilation of surface observations and soundings in the numerical weather modeling.

The paper presents results of SPINUA (Stable Point Interferometry over Unurbanised Areas) Persistent Scatterers Interferometry (PSI) processing chain to study Earth surface deformations along the SW coast of the Gulf of Gdañsk, along the SE part of the Baltic Sea. As the input for SPINUA techniques 40 descending ERS-1/2 SLC (Frame = 251, Track = 36) images from the period 1995-2001 has been used. The area of interest (AOI) includes few cities and several towns, villages and harbors. The low lying coastal areas of the SW part of the Gulf of Gdañsk are at risk of floods and marine erosion. The PSI results, however, did not reveal the presence of a regional scale, spatially consistent pattern of displacements. It is likely that any crustal deformations in the AOI simply do not exceed ±2 mm/year, which is the velocity threshold we assumed to distinguish between moving and non-moving persistent scatterers (PS). Importantly, for the most part the urban areas of the main cities (Gdañsk, Gdynia and Sopot) results show ground stability. Nevertheless, significant downward movements up to several mm/year, are locally noticed in the Vistula river delta - alluvial plain system located in the coastal zone east of Gdañsk as well as in the inland area west of the Gdañsk city. Indeed, the highest subsidence rates (-12 mm/year) was observed in the Gdañsk petroleum refinery constructed on alluvial sediments. Thus the anthropogenic loading and consolidation of the recent deposits can locally be an important factor causing ground subsidence.

A relevant part of the Assisi urban area (central Italy), built up after 1950 and located outside of the ancient town center, is interested by a landslide characterized by a rather slow rate of movement, which has caused important damages to buildings for an accumulation effect in the years. The movements of the soil surface have both a horizontal and a vertical component. For the monitoring of the landslide behaviour, the determination of the motion field and its evolution in time, a precision GNSS network has been established over the area since 1995, connecting by means of a baseline network the moving area with stable geologic formations located well outside (up to some km distance) of the landslide body. Further (1999), a leveling network has been added to improve the definition of the vertical component of the motion field. Surveys of both GNSS and leveling networks have been carried out in time, with an approximately annual cadence, until the actuality. Time series of coordinates and heights spanning along the observation period (1995-2010) are hence available for the network points. The Assisi landslide area has also been investigated by means of SAR: the data here presented derive from the analysis of Envisat data spanning in time from 2003 to 2010, thus with a 7-years overlapping with the GNSS and leveling surveys, which make possible a comparison. SAR data refer to scatter points which are numerous and well spread over the landslide area but almost never coinciding with the GNSS and leveling markers. Moreover, the type of movements which can be put into evidence are different: along an assigned direction (the LOS, Line Of Sight) from the SAR data, in 3 dimensions from GNSS, along the vertical direction from leveling. This paper presents a comparison of the SAR results with the GNSS data, from which the LOS component has been derived. The comparison has been made for each GNSS marker with the surrounding SAR scatters, trying to take into account local topological effects when possible. A good correspondence between the results of the different techniques has been found in many cases, and a deeper analysis of the movement field has been possible.

The Multi-Chromatic Analysis (MCA) uses interferometric pairs of SAR images processed at range sub-bands located at different spectrum positions, and explores the phase trend of each pixel in the frequency domain. By exploring the linear phase trend along the sub-bands frequencies, both phase unwrapping as well as height computation can be performed on a pixel by pixel basis without spatial integration. This work is aimed at experimenting a further application of MCA consisting in processing a single SAR acquisition for measuring the optical path between the SAR sensor and the imaged scene. We used TerraSAR-X SAR data acquired in Spotlight mode over the Venice Lagoon, and took advantage of corner reflectors already deployed for other purposes which guarantee phase stability as well as precise geographical positioning. We computed the delay induced by the atmosphere on the SAR signal, then compared this measure with that derived by analytical models and in situ records.

High resolution numerical weather models (NWM) are being to play a role of increasing importance for atmospheric phase screen (APS) mitigation. Here we present preliminary investigations concerning the estimation of the atmospheric contribution to X-band InSAR phase fields through numerical weather modeling. We selected tandem-like pairs of Stripmap COSMO/SkyMED images acquired over Parkfield (California, USA) with short normal baselines, thus ensuring low sensitivity to elevation. By using a 30m SRTM DEM available for the area of interest, we generated differential phase fields, mainly related to the difference between atmospheric conditions at the times of the two acquisitions. The interferometric artifacts have been hence compared to independent estimates of the atmospheric phase delay introduced by both wet and dry the components of the troposphere, obtained through Regional Atmospheric Modeling System (RAMS), a finite-difference, primitive equation, three-dimensional mesoscale NWM originally developed at Colorado State University. RAMS is a prognostic model capable of simulating a wide range of atmospheric motions due to the use of a nested grid system. Incorporation of topographic features occurs through the use of a terrain-following vertical coordinate system, while turbulence is parameterized using Mellor and Yamada's level 2.5 scheme, as modified by Helfand and Labraga for growing turbulence. In order to assess the impact of the boundary conditions, numerical simulations have been repeated by using GFS, ECMWF and NAM data (resolution: 0.5 deg, 0.25 deg and 12km respectively). A spin-up time exceeding 24h was necessary for ensuring a realistic computation of the atmospheric boundary layer depth. Finally, the 3D computation of the scaled-up refractive index and its integration along the Line-Of-Sight (LOS) of the SAR sensor was performed in order to estimate the two-way radar phase delay. The preliminary results confirm the indications coming from recent similar studies: weather models are good for the long wavelengths (>20 km) and for vertical stratification which depends on the hydrostatic component of the troposphere, while they cannot actually ensure a sub-centimetric accuracy in the estimation of the wet component, as instead required in X-band interferometry. Finally, we used the GPS daily RINEX available on the Parkfield area to infer the atmospheric Zenith Total Delay (ZTD) and validate the outcomes of the NWM. GPS data were processed at ASI/CGS by using the NASA/JPL GIPSY-OASIS II for data reduction. The Precise Point Positioning approach was applied fixing JPL fiducial-free satellite orbits, clocks and earth orientation parameters, IGS absolute phase center variations and estimating, with a cut-off angle of 7deg, site coordinates, station clock, phase ambiguities, ZTD and tropospheric gradients. ZTD and tropospheric gradients are modeled as random walk processes and estimated with a sampling rate of 5 minutes. Results show correlation between the values computed by NWM and GPS. Furthermore, the differences are not correlated with the topography thus suggesting that the main cause of the mismatches relies on the tropospheric turbulence. This further confirms our previous conclusions.

A relevant part of the Assisi urban area (central Italy), built up after 1950 and located outside of the ancient town center, is interested by a landslide characterized by a slow rate of movement, still causing important damages for an accumulation effect in time. For the monitoring of the landslide behaviour, the determination of the motion field and its evolution in time, a precision GNSS network has been established over the area since 1995, connecting by means of a baseline network the moving area with stable geologic formations. Further (1999), a leveling network has been added to improve the definition of the vertical component of the motion field and the density of controlled points. Surveys have been carried out until the actuality. Time series of coordinates and heights spanning along the observation period (1995 or 1999 to 2010) are hence available for the network points. The Assisi landslide area has also been investigated by means of InSAR: the data here presented derive from the analysis of Envisat data spanning in time from 2003 to 2010, thus with a 7-years overlapping with the GNSS and leveling surveys, which make possible a comparison. SAR data refer to scatter points which are numerous and well spread over the landslide area but almost never coinciding with GNSS and leveling markers. Moreover, the type of movements which can be put into evidence are different: along an assigned direction (LOS) from the SAR data, in 3 dimensions from GNSS, along the vertical direction from leveling. This paper presents a comparison of the InSAR results with the GNSS data, from which the LOS component has been derived. The comparison has been made for each GNSS marker with the surrounding SAR scatters, trying to take into account local topological effects when possible. A comparison between InSAR and leveling data requires a different approach, considering the different one-dimensional components of the movement, vertical for leveling and oblique (along the LOS) for InSAR.

COSMO/SKYMED is currently the unique constellation of synthetic aperture radar (SAR) sensors operative, which is also for civilian use. On April 6, 2009, an Mw 6.3 earthquake struck the city of l’Aquila in Central Italy. The constellation acquired data stacks over the hit area at an unprecedented temporal rate. In this letter, the results obtained by processing several data set via two independent multitemporal differential interferometric SAR techniques are presented to demonstrate the capability of this constellation in postseismic deformations monitoring.

L'osservazione della Terra da piattaforme spaziali, integrata con misure in situ e con acquisizione da piattaforme aeree, è una tecnologia di riferimento per il monitoraggio di ampie zone del Territorio con una elevata frequenza spaziale. Queste ca-ratteristiche sono essenziali per investigare, da un lato, l'effetto di modifiche indotte da cambiamenti climatici, dall'altro la presenza di situazioni che siano precursori di cambiamenti, in un'ottica di previsione ed allerta. Nel presente lavoro vengono presentati alcuni esempi applicativi in questo scenario.

The recent availability of wide-bandwidth, high-frequency, high-resolution SAR data is contributing to improved monitoring capabilities of spaceborne remote sensing instruments. In particular, the new COSMO/SkyMed (CSK) and TerraSAR- X (TSX) X-band sensors allow better performances in multitemporal DInSAR and PSI applications than legacy C-band sensors such as ENVISAT ASAR, with respect to both target detection and terrain displacement monitoring capabilities. In this paper we investigate about the possibility of achieving performances of PSI displacement detection comparable to those of C-band sensors, by use of reduced numbers of high-resolution X-band acquisitions. To this end, we develop a simple model for phase and displacement rate measurement accuracies taking into account both target characteristics and sensors acquisition schedule. The model predicts that the generally better resolution and repeat-time characteristics of new-generation X-band sensors allow reaching accuracies comparable to C-band data with a significantly smaller number of X-band acquisitions, provided that the total time span of the acquisitions is large enough. This allows in principle to contain the costs of monitoring campaigns, by using less scenes. Indications are more variable in the case of short-time acquisition schedules, such as those involved in the generation of so-called "rush products" for emergency applications. In this case, the higher uncertainty given by shorter total time spans lowers X-band performances to levels mostly comparable to those of the legacy medium-resolution C-band sensors, so that no significant gain in image number budget are foreseen. These theoretical results are confirmed by comparison of three PSI datasets, acquired by ENVISAT ASAR, CSK and TSX sensors over Assisi (central Italy) and Venice.

In the present work we describe a new and alternative repeat-pass interferometry algorithm designed and developed with the aim to: i) ncrease the robustness wrt to noise by increasing the number of differential interferograms and consequently the information redundancy; ii) guarantee high performances in the detection of non linear deformation without the need of specifying in input a particular cinematic model. The starting point is a previous paper dedicated to the optimization of the InSAR coregistration by finding an ad hoc path between the images which minimizes the expected total decorrelation as in the SABS-like approaches. The main difference wrt the PS-like algorithms is the use of couples of images which potentially can show high spatial coherence and, which are neglected by the standard PSI processing. The present work presents a detailed description of the algorithm processing steps as well as the results obtained by processing simulated InSAR data with the aim to evaluate the algorithm performances. Moreover, the algorithm has been also applied on a real test case in Poland, to study the subsidence affecting the Wieliczka Salt Mine. A cross validation wrt SPINUA PSI-like algorithm has been carried out by comparing the resultant displacement fields.

The present paper presents the results of the application of Multi Chromatic Analysis (MCA) for height retrieval by processing both AES-1 airborne data and satellite TerraSAR-X data. In particular, a test of the robustness of the MCA technique with respect to total processed bandwidth has been performed through comparison of results from datasets with bandwidths spanning form 100 to 400 MHz. A first validation of the mentioned technique has been carried out by comparing the retrieved heights w.r.t. ground elevation from external SRTM DEM, as well as by verifying the reliability of the fringe classifications based on the integer number of phase cycles computed through MCA. Results are presented and commented by addressing potential and limitation of the technique.

This work presents first results of interferometric processing of ALOS PALSAR Single Look Complex SAR images (Fine Beam Mode), concerning ground deformations in the Wieliczka Salt Mine area, a few km from Cracow, Poland. It follows a recent Persistent Scatterers SAR Interferometry (PSI) analysis on this area, obtained by processing several tens of ERS satellite images covering the period 1992-2000. ERS results revealed the presence of a few kilometres long, slowly subsiding zone corresponding very well to the extent of the underground salt mine. The present work aims to extend the analysis by exploiting ALOS-PALSAR data especially for the rural areas, which neighbour the salt mine but lack PS in C-band, relying on the lower sensitivity to temporal decorrelation of L-band w.r.t. C-band radar data. This work shows and compares ERS and PALSAR (Fine Beam) ground displacement patterns detected over the Wieliczka Salt Mine area through the application of multi-temporal interferometric techniques.

A partire dagli ultimi decenni, la linea di costa del Tavoliere di Puglia è interessata da un forte arretramento. In concomitanza con intensi eventi meteo-marini si è spesso registrata una profonda ingressione delle acque nell'entroterra. Questi fenomeni frequenti, uniti alla presenza di lesioni da cedimenti su strutture antropiche, indicano la presenza di subsidenza su un'area non limitata alla sola fascia costiera. Per analizzare l'evoluzione recente del fenomeno e determinarne i tassi è stata applicata la tecnica PSI (Persistent Scatterers Interferometry), che permette di ottenere mappe di spostamenti millimetrici della superficie terrestre da lunghe serie di interferogrammi radar, disponibili con una frequenza di circa 1 acquisizione ogni 35 giorni. L'analisi è ristretta a oggetti con forti segnali di ritorno, che generalmente coincidono con manufatti antropici. In totale sono state analizzate 103 immagini acquisite dai satelliti ERS-1/2 ed ENVISAT, riferite a periodi di acquisizione tra gli anni 1995 e 2000 (ERS) e 2003-2008 (ENVISAT). I risultati indicano la presenza di una deformazione che interessa l'intero intervallo temporale analizzato, spazialmente distribuita a formare una depressione lentiforme centrata sul villaggio turistico Ippocampo, con velocità medie superiori a 20 mm/a e trend in aumento negli ultimi anni. L'analisi comprende una prima validazione di questi risultati attraverso attività in situ, nonché una pianificazione per un'integrazione delle osservazioni con dati sulle aree più interne del Tavoliere.

This work builds upon the earlier Persistent Scatterers SAR Interferometry (PSI) study of the Wieliczka area [1], focused on the detection of long-term subsidence caused by the activity of the ancient Wieliczka Salt Mine (Unesco Heritage Site, Poland). The SPINUA processing of several tens of ERS images covering the period 1992-2000 has led to the identification of over 3000 radar targets (density about 100 PS/km2) and shown that the subsiding zone (movements up to 24 mm/yr) corresponds well to the subsurface extent of the salt deposit and mine works. The Wieliczka area is characterized by a range of ground instability phenomena (subsidence, landslides, slope creep), as well as variable geological, geomorphological and land cover conditions, and hence offers an excellent opportunity to test the practical applicability of multi-temporal differential interferometry techniques. Here we extend the study to the peri-urban and rural areas surrounding the town of Wieliczka and explore the utility of C-band PSI to investigate landslides and related ground instability phenomena. Furthermore, we provide a more in depth interpretation of the satellite-borne observations by supplementing the PSI data with in situ information, including also the data from a local geodetic network consisting of over 1000 benchmarks. It is shown that i) the PSI-detected ground displacements agree very well with the levelling results and provide useful complementary data (increased density of measurements); ii) a very small percentage (below 3%) of PS falls within the landslide limits (in relation to the low degree of urbanization of failure-prone slopes and presence of vegetation) and relatively little information can be obtained on slope movements. Furthermore, there is a concentration of large, pre-existing landslides that originate on the north-facing slopes of the Carpathian overthrust front and descend towards a few km long subsidence bowl in the central-western part of Wieliczka. The toes of some landslides include several slowly moving PS (within 1 cm/yr), but since they also overlap the southern part of the subsidence bowl, no straightforward interpretation of the causative processes and relative hazard assessment are possible without high precision data on the horizontal component of motion. It should be useful to fulfill this additional data requirement (e.g. by installing a local GPS network), because the affected area includes buildings and roads that have already suffered damage in the past. Regardless of the exact cause(s) of the observed PS displacements, the case of concentrated large slides suggests that the changes in the Wieliczka morphology, linked to the subsidence induced by centuries of mining (lowering of slope base and hence steepening), have been responsible for the long-lived landsliding on slopes facing the mine area. Acknowledgements The ERS images were provided by ESA under the ALOS ADEN 3595 project. The efforts of JW and MG were supported by the Executive Programme of Scientific and Technological Co-operation between the Republic of Poland and the Italian Republic (project No. 16, TS). We also thank Z. Zarebski, A. Trzoslo and P. Ulmaniec of the Wieliczka Salt Mine for providing ground information. References [1] J. Wasowski, F. Bovenga, R. Nutricato, D. Conte, A. Refice, Z. Kowalski, and M. Graniczny. 2008. Satellite Interferometry Reveals Spatial Patterns of Subsidence in the Ancient Wieliczka Salt Mine (UNESCO Heritage Site, Poland), Proceedings of FRINGE 2007 Workshop, Frascati, Italy, 26-30 Novembre 2007, ESA SP-649, February 2008 - CDROM.

We present results of an experiment aimed at detecting possible displacements due to subsidence in the coastal area of the Tavoliere plain, Puglia Region, in Southern Italy, through analysis of remotely sensed data. The Tavoliere is the second largest Italian plain. Its coastal area, between the urban centers of Manfredonia and Barletta, is composed of a 50 km long sandy beach (Manfredonia gulf), linking the Gargano massif at north with the Murge plateau in the south-east. Both areas belong to the carbonate Mesozoic Apulian platform. The current configuration of the Gulf was reached recently, as a consequence of the Holocene sea level rise. During the Neolithic age the plain was occupied by an elongated lagoon (Salpi Lagoon) [1]. During the 2nd century B.C., alluvial deposition caused the lagoon to be separated into two basins: the so-called Salpi lake at south and the Salso lake at north. To cope with the increasing demand of arable lands and with the necessity to make unhealthy areas accessible to humans, some reclaims were accomplished by diverting and channelling the rivers crossing the Tavoliere plain, and by levelling dune belts. At present, the beach is separated by low artificial dunes from the areas already reclaimed and intensely cultivated or exploited as evaporation basin for salt production. In the last decades, the coastal area has been retreating due to a reduction in sediment input necessary for coastal equilibrium. The levelling of dunes and the decrease of fluvial turbid discharge due to dam constructions are probably the cause of this deficit in sediment supply. During highly intense hydrodynamic and meteorological events, sea waters often penetrate deeply inland, flooding intensively cultivated areas. These events are occurring with growing frequency and rates. They are an indication of the possibility that those areas are subject to subsidence at a faster rate in comparison to the surroundings. An example is the salt marsh located inland of the tourist sea village "Ippocampo". Here, unpublished studies based on ground data indicate average subsidence rates of the order of 0.20 mm/y in the last 125 ka for the inland area next to the village. More recently, height maps issued by the Italian Military Geographic Institute (IGM) in the 1950s report heights a.s.l. of the order of a few m. Observing that today the area is practically at sea level, an average subsidence of the order of tens of mm/y can be inferred for the last 50 years. To gain insight into the recent evolution of these phenomena, we investigate vertical movements on the coastal Tavoliere area through multitemporal differential Interferometric synthetic aperture radar (DInSAR) techniques. We use a persistent scatterers interferometry (PSI) processing methodology [2] to estimate subsidence displacement rates from long temporal series of SAR acquisitions. PSI techniques, first developed at POLIMI [3], allow to retrieve phase information from stacks of co-registered SAR interferograms spanning many years and taken from different directions with large baselines, by restricting the analysis to selected image pixels containing single objects with strong radar backscatter returns. Exploiting the high temporal stability of radar returns from these targets, it is possible to correct the images from spurious phase contributions such as atmospheric phase artefacts and errors in the digital elevation models used to account for topographic InSAR phase. Such stable objects typically coincide with man-made features, so successful applications of PSI techniques are mainly reported over urban centers. We processed a total of 105 SAR images acquired from the ERS-1/2 and ENVISAT satellites, organized in 3 stacks related to both descending (50 ERS-1/2 scenes) and ascending (25 ERS-1/2 and 30 ENVISAT scenes) acquisition geometries. The acquisitions refer to the temporal periods from 1995 to 2000 (ERS) and 2003 to 2008 (ENVISAT), respectively, with a temporal repetition frequency of roughly 1 acquisition every 35 days. The 3 stacks, covering approximately the same ground area centred on the Tavoliere coastal plain, were processed independently. Reliable phase measurements were obtained over small urban centers and anthropogenic features scattered along the coast. Results from all 3 stacks indicate the presence of displacements occurring through the entire temporal interval of observation. In particular, displacements appear spatially organized as a subsidence "bowl" centered approximately around the area of Zapponeta, with maximum subsidence rates exceeding 20 mm/y. The detected displacements appear consistent with the average rates deduced heuristically from analysis of the environmental settings as exposed above. Moreover, they also qualitatively agree with other investigations performed using analogous techniques and data over the region (e.g. [4]). Possible interpretation of these results can be attempted by considering that the area has been repeatedly subject to reclaiming through filling, and that the deposited sediments are most exposed to compaction. Moreover, the area is subject to intense water extraction, which further enhances the effects of sediment compaction. Validation of the obtained measurements is in progress through extended data analysis and in situ activities. However, these preliminary analyses and comparisons between InSAR and ground data hint to the possible presence of two co-existing subsidence phenomena in the area: a natural subsidence due to tectonics or isostatic rebound, with slow subsidence effects occurring over geologic time scales, with an additional, more pronounced subsidence phenomenon on the recent sediment deposits due to sediment compaction under lithostatic loading, and an anthropogenic local, accelerated subsidence on the lowest areas, due to intensive draining mostly for irrigation purposes, which adds to recent land remediation actions to cause a worrisome lowering of the water table in the area. References [1] F. Boenzi, M. Caldara, M. Moresi, L. Pennetta 2002, "History of the Salpi lagoon-sabhka (Manfredonia Gulf, Italy)". Il Quaternario, 14, 93-104. 2001 [2] F. Bovenga, A. Refice, R. Nutricato, L. Guerriero, M.T. Chiaradia, "SPINUA: a flexible processing chain for ERS / ENVISAT long term interferometry", Proceedings of ESA-ENVISAT Symposium, Salzburg, Austria, 6-10 September, 2004. [3] Ferretti, A., Prati, C., Rocca, F. "Permanent Scatterers in SAR Interferometry". IEEE Transactions on Geoscience and Remote Sensing 39, 8–20, 2001. [4] S. Salvi, S. Atzori, C.A. Brunori, F. Doumaz, G.P. Ricciardi, G. Solaro, S. Stramondo, C. Tolomei, R. Lanari, A. Pepe, A. Ferretti, S. Cespa, "The VELISAR initiative for the measurement of ground velocity in italian seismogenic areas", EGU General Assembly, Wien, Austria, 15-20 April, 2007.

Persistent Scatterers Interferometry (PSI) and satellite radar imagery can be used to detect very slow displacements (mm-cm per year) of targets (PS) exhibiting coherent radar backscattering properties (mainly man-made structures). Here we present results of the PSI application to the Daunia Apennines, which include many hilltop towns affected by landslides. Examples from the towns Casalnuovo Monterotaro and Pietramontecorvino are used to illustrate that the interpretation of PS data on urbanised slopes can be diffi-cult, because their movements may arise from a variety of processes: i) volumetric strains within soils, ii) natural or anthropogenic subsidence or uplift, iii) settlement of engineering structures, iv) deterioration of man-made structures, v) extremely slow slope deformations that may or may not lead to failure. Where true landslide movements are detected, they likely regard long-term post-failure displacements involving clay-rich materials.